How to make an infinite scroll with react-query? - reactjs

Question

I'm trying to use react-query useInfiniteScroll with a basic API, such as the cocktaildb or pokeapi.
useInfiniteQuery takes two parameters: a unique key for the cache and a function it has to run.
It returns a data object, and also a fetchMore function. If fetchMore is called - through an intersection observer for exemple -, useInfiniteQuery call its parameter function again, but with an updated payload thanks to a native callback getFetchMore().
In the official documentation, getFetchMore automatically takes two argument: the last value returned, and all the values returned.
Based on this, their demo takes the value of the previous page number sent by getFetchMore, and performs a new call with an updated page number.
But how can I perform the same kind of thing with a basic api that only return a json?
Here is the official demo code:
function Projects() {
const fetchProjects = (key, cursor = 0) =>
fetch('/api/projects?cursor=' + cursor)
const {
status,
data,
isFetching,
isFetchingMore,
fetchMore,
canFetchMore,
} = useInfiniteQuery('projects', fetchProjects, {
getFetchMore: (lastGroup, allGroups) => lastGroup.nextCursor,
})

Answer 1

infinite scrolling relies on pagination, so to utilize this component, you'd need to somehow track what page you are on, and if there are more pages. If you're working with a list of elements, you could check to see if less elements where returned in your last query. For example, if you get 5 new items on each new fetch, and on the last fetch you got only 4, you've probably reached the edge of the list.
so in that case you'd check if lastGroup.length < 5, and if that returns true, return false (stop fetching more pages).
In case there are more pages to fetch, you'd need to return the number of the current page from getFetchMore, so that the query uses it as a parameter. One way of measuring what page you might be on would be to count how many array exist inside the data object, since infiniteQuery places each new page into a separate array inside data. so if the length of data array is 1, it means you have fetched only page 1, in which case you'd want to return the number 2.
final result:
getFetchMore: (lastGroup, allGroups) => {
const morePagesExist = lastGroup?.length === 5
if (!morePagesExist) return false;
return allGroups.length+1
}
now you just need to use getMore to fetch more pages.

Answer 2

The steps are:
Waiting for useInfiniteQuery to request the first group of data by default.
Returning the information for the next query in getNextPageParam.
Calling fetchNextPage function.
Reference https://react-query.tanstack.com/guides/infinite-queries
Example 1 with rest api
const fetchProjects = ({ pageParam = 0 }) =>
fetch('/api/projects?cursor=' + pageParam)
const {
data,
isLoading,
fetchNextPage,
hasNextPage,
} = useInfiniteQuery('projects', fetchProjects, {
getNextPageParam: (lastPage) => {
// lastPage signature depends on your api respond, below is a pseudocode
if (lastPage.hasNextPage) {
return lastPage.nextCursor;
}
return undefined;
},
})
Example 2 with graphql query (pseudocode)
const {
data,
fetchNextPage,
isLoading,
} = useInfiniteQuery(
['GetProjectsKeyQuery'],
async ({ pageParam }) => {
return graphqlClient.request(GetProjectsQuery, {
isPublic: true, // some condition/variables if you have
first: NBR_OF_ELEMENTS_TO_FETCH, // 10 to start with
cursor: pageParam,
});
},
{
getNextPageParam: (lastPage) => {
// pseudocode, lastPage depends on your api respond
if (lastPage.projects.pageInfo.hasNextPage) {
return lastPage.projects.pageInfo.endCursor;
}
return undefined;
},
},
);
react-query will create data which contains an array called pages. Every time you call api with the new cursor/page/offset it will add new page to pages. You can flatMap data, e.g:
const projects = data.pages.flatMap((p) => p.projects.nodes)
Call fetchNextPage somewhere in your code when you want to call api again for next batch, e.g:
const handleEndReached = () => {
fetchNextPage();
};
Graphql example query:
add to your query after: cursor:
query GetProjectsQuery($isPublic: Boolean, $first: Int, $cursor: Cursor) {
projects(
condition: {isPublic: $isPublic}
first: $first
after: $cursor
) ...